\section{batteries}
\paragraph{syntax extension}

Not of too much use , \textbf{Never use it in the toplevel}
\begin{itemize}
\item comprehension (M.filter, concat, map, filter\_map, enum, of\_enum) \\
  since it's at preproccessed stage, you can use some trick \\
  \verb|let module Enum = List in | will change the semantics \\
  \verb|let open Enum in| doesn't make sense, since it uses qualified name inside
\end{itemize}
\subsection{Dev}
\begin{itemize}
\item make changes in both .ml and .mli files
\end{itemize}
